Composite bodies containing organic polymers are well known to the art. Generally speaking, polymer composites, which may be regarded as multiphase materials of two or more components in which the polymer comprises the continuous phase, can be considered as containing fillers or reinforcing agents, the function of the two frequently overlapping. Thus, polymer composites have conventionally consisted of a base polymer containing additives such as plasticizers, colorants, flame retardants, reinforcing fibers and/or whiskers, fillers, and stabilizers against heat and/or sunlight. Polymer cements constitute another type of composite wherein the continuous phase is ceramic and the properties exhibited thereby are essentially those of a modified ceramic rather than a modified polymer. For example, a polymer is allowed to diffuse into the cement and is then polymerized in situ. Hence, polymer composites have typically been considered as being prepared from materials of two separate origins which have been physically produced by dispersing one phase in a continuous matrix of another phase.
However, there is a further class of materials involving combinations of polymers which have been termed polymer alloys or blends. In addition to one phase being fluid at some time in the preparation, as with conventional composites, in polymer alloys the second phase can also be fluid, either as a melt or as a polymerizing monomer. In this way a range of structures can arise. In addition, alloys provide a facility which conventional polymer composites cannot, in that the opportunity for phase reversal or inversion is presented, depending primarily, but not entirely, on the relative concentrations of the two polymers, inasmuch as the relative viscosity at the fabrication temperature is also important. Thus, from a state wherein one component is continuous in phase, a polymer alloy can comprise a system which is continuous with respect to the second phase or one in which both phases are continuous. Hence, one component can become enclosed in the second component and vice versa. Accordingly, where the properties of the two polymers are different, extreme changes in mechanical behavior can be experienced in the alloy vis-a-vis the starting components.
Alloys consisting of a combination of two or more polymeric resin systems where at least one of the polymers is present in a concentration greater than 5% by volume are well known to the art. Hence, alloys are mixtures of two or more resins which are blended, customarily in the molten state, to form new materials. Unlike copolymers, grafts, or interpenetrating polymer networks, no chemical synthesis or formation of new covalent bonds need occur. Alloys have been designated as either miscible or immiscible depending upon the number of phases present. To illustrate:
Miscible or soluble blends comprise one phase with one glass transition temperature (Tg). Individual polymer segments are intimately blended with some specific chemical or physical attraction taking place between dissimilar polymer chains, e.g., hydrogen bonding or donor-acceptor. In contrast, immiscible alloys consist of two or more discrete phases (continuous and disperse) and two or more Tgs. Completely immiscible alloys have limited product potential, however, inasmuch as delamination of materials is hazarded during processing because of lack of adhesion at the polymer interface.
Most commercially-marketed resin alloys are formed via some type of melt mixing utilizing a continuous-type intensive mixer or an extruder. Thus, two or more polymers in pellet or powder form are generally premixed or metered into an extruder, either a single screw or a multiscrew extruder, or into a continuous-type intensive mixer, fluxed for a brief period, and then shaped into pellets from strands or being diced from sheet.
Inorganic glasses can exhibit many desirable properties; for example, high elastic modulus, abrasion resistance, stain resistance, thermal stability, inertness to solvents, low coefficient of thermal expansion, and low permeability to moisture and gases. On the other hand, organic polymers can demonstrate such advantageous characteristics as high elasticity, flexibility, toughness, light weight, and ease in shaping, which properties are generally lacking in inorganic glasses.
As was noted above, filled plastic products are commercially available. Those products customarily consist of organic polymers enveloping discrete organic or inorganic particles, flakes, fibers, whiskers, or other configurations of materials. These filler materials may be incorporated principally for the purpose of reducing the overall cost of the product without seriously undermining the properties of the polymer. For example, clays and talc have been added as inexpensive fillers. On the other hand, the filler materials may be included to impart some improvement to a particular physical property exhibited by the polymer. For example, ceramic and glass fibers have been entrained in polymer bodies to provide reinforcement thereto. The strength demonstrated by those products is primarily dependent upon mechanical bonding between the inorganic fibers and the organic polymers.
Within the past two decades some research has been conducted to investigate the possibility of forming composite bodies consisting of inorganic glasses exhibiting low transition temperatures and organic polymers, which bodies would, desirably, demonstrate the combined properties of glass and plastic. Illustrative of that research is U.S. Pat. No. 3,732,181. As is observed there, the decomposition temperatures of known thermoplastic and thermosetting resins are so low that glass compositions wherein SiO.sub.2 is the principal network or glass former cannot be employed. Hence, to be operable, the Tg of the glass will be below 450.degree. C., and preferably below 350.degree. C. (As customarily defined, the Tg of a glass is the temperature at which increases in specific heat and coefficient of thermal expansion take place which are accompanied by a sharp drop in viscosity. This temperature is frequently deemed to lie in the vicinity of the glass annealing point.) That temperature limitation led to the use of glasses wherein P.sub.2 O.sub.5 and/or B.sub.2 O.sub.3 comprises the primary glass forming component. It is further explained there that, whereas thermoplastic resins have been principally investigated for use in glass-plastic composite articles, thermosetting resins which can be obtained as heatsoftenable precursors are also operable. Such resins can be blended with the glass into composite bodies with the re-shaping and final heat curing being completed in a single operation. As preferred thermoplastic polymers, the patent listed high density polyethylene, polypropylene, polystyrene, polymethyl methacrylate, poly-4-methylpentene1, polyethylene terephthalate, polycarbonates, polysulfones, polyvinyl chloride, and polytetrafluoroethylene. Acid sensitive polymers can be subject to degradation when in contact with glass and, hence, are warned against. Polyamides are noted as being particularly susceptible to that problem, with polyesters being less so.
U.S. Pat. No. 3,732,181 describes seven general methods wherein glass in the form of fibers, films, flakes, powders, or sheets is combined with a polymer and that composite is fashioned into a desired configuration through a variety of shaping means including compression molding, drawing, extrusion, hot pressing, injection molding, and spinning. The patent states that the ratio polymer:glass may range from 0.1:99.9 to 99.9:0.1 on a volume basis, but also observes that the concentration of glass in the polymer typically ranges about 5-66% by volume.
Finally, U.S. Pat. No. 3,732,181 discloses three broad areas of glass compositions exhibiting properties assertedly rendering the glasses suitable for use in glass-plastic composite articles:
(a) PbO+P.sub.2 O.sub.5 .gtoreq.95 mole %, wherein PbO constitutes 20-80 mole %;
(b) PbO+R.sub.2 O (alkali metal oxides)+P.sub.2 O.sub.5 .gtoreq.95 mole %, wherein PbO comprises 5-60 mole %, R.sub.2 O constitutes 5-35 mole %, and P.sub.2 O.sub.5 is present up to 85 mole %; and
(c) PbO+R.sub.2 O+B.sub.2 O.sub.3 +P.sub.2 O.sub.5 .gtoreq.95 mole %, wherein PbO comprises 5-30 mole %, R.sub.2 O constitutes 5-30 mole %, B.sub.2 O.sub.3 composes 5-20 mole %, and P.sub.2 O.sub.5 makes up 15-85 mole %.
The above composition intervals specify the required presence of PbO, but the patent avers that part or all of the PbO may be replaced with divalent metal oxides, noting in particular the alkaline earth metals and zinc.
A study of that patent, however, uncovers no description of products wherein the glass phase and the polymer phase become co-continuous, or where particles of each phase are simultaneously enclosed within larger regions of another phase, this phenomenon being termed localized phase inversion/reversal. Nor is there any description of bodies wherein the glass and polymer demonstrate at least partial miscibility and/or a reaction therebetween such that the two components are intimately blended together. Nor is there any description of bodies exhibiting an essentially uniform, fine-grained microstructure wherein the glass and polymer elements comprising the microstructure are of relatively uniform dimensions. Contrariwise, U.S. Pat. No. 3,732,181 specifies the presence of fibrils, flakes, rods, strands, and/or spheres of one component in a matrix of the second component. Hence, the patent describes products having the microstructure more akin to that of a conventional filled glass-plastic composite, rather than to that of an alloy.
Experience in the glass composition art has indicated that borate-based and phosphate-based glasses normally exhibit poorer chemical durability and resistance to moisture attack than silica-based compositions, and that failing becomes even more exacerbated as such glasses are formulated to demonstrate lower transition temperatures. For example, phosphate-based glasses manifesting a low Tg are commonly degraded when exposed to atmospheres of high humidity and, not infrequently, are actually hygroscopic. This lack of resistance to attack by moisture frequently encountered in phosphate-based glass compositions is evidenced in the rate of dissolution data provided in U.S. Pat. No. 3,732,181 with respect to the glasses utilized in the working examples. Because of this poor resistance to chemical and moisture attack evidenced by phosphate-based and borate-based glasses having a low Tg, glass-plastic composite articles fabricated from glasses and polymers which are thermally co-deformable at similar temperatures have not been marketed to any substantial extent. Thus, whereas the glass-plastic composite articles known to the art are not porous in a physical sense, the polymers are permeable to water; which permeability permits water to migrate into the article and thereby come into contact with the glass particles. And, because of the high surface area of the glass flakes, fibers, powders, and the like present in the composite articles, degradation thereof can proceed rapidly. That situation becomes more pronounced as the proportion of glass in the composite is increased. Yet, to produce articles exhibiting high stiffness, high hardness, and good mechanical strength, the glass component should constitute the greater proportion thereof.